The present invention relates to an optical cross-connect having at least one controllable switching module which has optical inputs and outputs.
Optical transmission networks based on high bit-rate, fiber transmission paths with optical cross-connects, and possibly also with optical frequency multiplexing, represent the future transport network for transmission of large amounts of data for future telecommunication.
The growth to be expected in the field of data transmission via optical transmission networks, particularly as a result of the increase in Internet access providers and Internet users, makes it necessary to design such optical transmission networks such that they can be scaled as easily as possible by their operators. That is to say, the upgrade capability of an optical cross-connect and the linking of additional users to widely differing connection requirements must be extremely flexible, and must be feasible within a very short time and with a reasonable level of technical complexity.
In this case, with regard to optical cross-connects that are in the form of fiberoptic distribution panels, optical connections are implemented in such a way that optical connections are passed on manually, such as via an optical plug connection, in the respective optical cross-connects. For this purpose, two optical conductors, which each have a plug connection, are connected to one another via such an optical plug connection, with the optical plug connection having an optical connecting conductor and two plugs, which are fitted to each of the ends of the optical connecting conductor. The plugs for the optical connecting conductor are inserted into the optical connections of the optical conductors that are to be connected which results in an optical connection between a first optical conductor or a supply line fiber and a second optical conductor or an output fiber. In order to reduce the probability of a manual incorrect configuration of the optical connection or of the optical plug connection, DE 19920452 discloses an optical plug connection which, in addition to the optical plug connection, has an electrical connection for verification of the optical plug connection. In this case, the configuration of the optical plug connection is indicated to the network management system, with the aid of the additional electrical connection, as soon as the optical connection is made. Furthermore, if required, the network management system can determine the present configuration state of each optical plug connection at any time. Such optical cross-connects, which are in the form of fiberoptic distribution panels, cannot be controlled, however, via a central control unit or the network management system, so that an enormous amount of effort, in terms of both time and money, is required to produce an optical connection due to the manual actions required for this purpose by specialist personnel on the optical cross-connect. For this reason, static connections are normally set up via an optical cross-connect designed in this way in order to keep the financial cost of manual configuration of the optical cross-connect as low as possible.
Controllable optical cross-connects or switching modules are known for producing dynamic optical connections; that is to say optical connections which are reconfigured a number of times within one day. For example, in this context, see, in particular, DE 4314354, in which switching matrices are provided with the aid of optical switches. This allows optical connections to be connected electronically via a network management system, thus avoiding the manual xe2x80x9cinsertionxe2x80x9d of an optical connection, which often takes a long time. However, one disadvantage is that expansion, which is the increasing of the number of optical interfaces in the optical automatically controllable cross-connect or switching module, can be achieved only by a disproportionate increase in the equipment complexity. If, by way of example, it is intended to double the number of optical interfaces in a controllable optical cross-connect, then the optical switching modules in the switching matrix must be cascaded in order to ensure minimum freedom from blocking in the controllable switching module. In some circumstances, depending on the required freedom from blocking for the controllable switching module, such cascading in order to double the number of optical interfaces can lead to the number of optical switching modules being more than quadrupled. In addition, the cascading of optical switching modules increases the forward loss in the optical cross-connect, so that additional regeneration of the optical signal which is transmitted via the optical cross-connect or the cascade of controllable switching modules may be necessary.
An object of the present invention is to provide an optical cross-connect of the type mentioned initially such that the equipment complexity for connecting optical connections as required between the inputs and outputs of an optical cross-connect is reduced.
The major aspect of the optical cross-connect according to the present invention is that a distribution rack is provided which can be monitored via a network management system and has external and internal optical distribution inputs and distribution outputs, and whose external and internal optical distribution inputs and distribution outputs can be connected within the distribution rack via a number of optical connecting conductors, which each have an additional electrical conductor for verification of the optical connection. Furthermore, according to the present invention, a number of the internal optical distribution outputs are connected to the inputs of the controllable switching module, and the outputs of the controllable switching module are connected to a number of internal optical distribution inputs, with the controllable switching module being controlled taking account of the optical connections which are verified by the network management system. The verification of the connected or inserted optical connection within the distribution rack by the network management system advantageously results in up-to-date information about the configuration of the optical cross-connect, and this can be used for controlling the controllable switching module. Thus, it is possible for the network administrator, which serves the network management system, to pass on dynamic connections within a very short time, without the servicing personnel having to manually produce the optical plug connections required for this purpose, on the optical cross-connect, which is generally installed several kilometers away. In consequence, depending on the proportion of the dynamic optical connections in the total number of optical connections which can be connected via the optical cross-connect, it is possible to control the number of automatically controllable switching modules or optical interfaces as required; that is to say, if the requirement for automatically controllable optical interfaces in the optical cross-connect increases, then further controllable switching modules can be connected between the internal distribution inputs and distribution outputs of the distribution rack. Thus, it is possible, in a particularly advantageous manner, to increase the number of optical connections which can be connected in the optical cross-connect according to the present invention, with only a small amount of equipment complexity.
According to a further embodiment of the optical cross-connects according to the present invention, information about the optical connections which are connected from external optical distribution inputs to internal optical distribution outputs, and about the optical connections which are connected from the internal optical distribution inputs to external optical distribution outputs is available to the network management system on the basis of the verification, these optical connections being the connections which are taken into account in order to control the controllable switching module such that, in order to automatically pass on an optical connection from a specific external optical distribution input to a specific external optical distribution output, the internal optical distribution output which is connected to the specific external optical distribution input via an optical connection, and the internal optical distribution input which is connected to the specific external optical distribution output via a further optical connection, are determined with the aid of the network management system, and the determined internal optical distribution output is passed on to the determined internal distribution input with the aid of the controllable switching module. For a connection request between an external optical distribution input and an external optical distribution output and/or supply line/output fibers connected to them, the present optical connection for the respective internal optical distribution input or output can be determined by the network management system, and the desired connection then can be passed on via the controllable switching module. In consequence, dynamic optical connections from an optical supply line fiber can be passed on in a particularly advantageous manner as required to different optical output fibers. In this case, the network management system can monitor the internally connected optical connection before the switching process.
According to the present invention, the optical cross-connect has optical interfaces which are provided for connection of the external optical distribution inputs of the distribution rack to optical supply line fibers, and of the external optical distribution outputs to optical output fibers. Furthermore, according to the present invention, the external and internal optical distribution inputs and distribution outputs of the distribution rack are in the form of combined optoelectrical connections. The configuration of the external and internal optical distribution inputs and distribution outputs as combined optoelectrical connections, according to the present invention, allows for the present configuration of the inserted optical connections in the distribution rack to be accessible to the network management system; that is to say, the electrical connection to be set up in addition to the optical connection in the distribution rack can be monitored by the network management system.
According to a further embodiment of the optical cross-connect, a number of controllable switching modules also may be connected in parallel and/or in series in order to enlarge the automatically controllable optical interfaces of the optical cross-connect. The connection of a number of controllable switching modules in parallel according to the present invention allows the number of optical connections which can be connected dynamically by the network management system within the optical cross-connect to be produced with the equipment complexity being minimized. In addition, the connection, according to the present invention, of the controllable switching modules to internal optical distribution inputs and distribution outputs allows the connection configuration of the supply line/output fibers to be retained in a particularly advantageous manner when a number of controllable switching modules are added to the optical cross-connect. That is, the circuitry for the external optical distribution inputs and distribution outputs can be retained, and the reconfiguration of the optical connections within the distribution rack which is required for the expansion is carried out on the internal optical distribution inputs and distribution outputs and in the network management system. This allows the migration of so-called xe2x80x9chigh dynamic islandsxe2x80x9d to be implemented within an existing optical cross-connect with considerably reduced equipment complexity.
Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the Figures.